The Britain-based watchdog, which uses a countrywide network of activists and doctors to compile its tolls, said at least 123 people were killed on Tuesday, including some 30 in and around Damascus.

Damascus has now become the focus of clashes. President Bashar al-Assad's forces on Tuesday blasted a string of rebel zones on the eastern and southwestern outskirts of the city.

"The air force is bombarding Mleha and Zabdine" in southeast Damascus, the Observatory said, adding that Daraya to the southwest was under artillery fire, amid clashes at Saqba to the east.

Battles east of Damascus have grown especially bloody as troops try to push back rebels in the Eastern Ghouta region who have inched closer towards the capital.

Warplanes on Wednesday overflew the area, through which passes the road to Damascus international airport.

The watchdog also reported security force swooped on several areas in the city centre.

More than 41,000 people have been killed as the Syrian conflict approaches the 21-month mark, according to the Observatory.

Al-Watan, a daily close to the government, said on Wednesday the army "continues to hunt armed groups along the road to the international airport, killing or wounding dozens of terrorists" -- the regime's term for rebels.

In the northwest, seven soldiers were killed in "a rebel attack on a checkpoint south of Maaret al-Numan on the Aleppo-Damascus road," the Observatory said.

There was also fighting around the Wadi Deif military base, which has been under siege since rebels took Maaret al-Numan in October, it reported.

The clashes come a day after NATO approved member state Turkey's request for Patriot missiles to defend its border following a series of warnings to Damascus not to use chemical weapons.

On Monday, US President Barack Obama warned Assad against using chemical weapons, saying there would be "consequences" for such an action.